grep
search file or standard input for lines containing a match to regular expression regex. by default,matching lines will be displayed and nonmatching line will not be displayed. when multiple files are specified, grep displays the filename as a prefix to the output lines( use the -h to suppress filename prefixes)
-c display only a count of matched lines,but not the lines themselves
-h display matched lines.but don't include filename for multiple file input
-i ignore uppercase and lowercase distinction. allowing abc to match both abc and ABC.
-n display matches lines prefixed with their line numbers. when used
with multiple files.both the filename and line number are prefixed
-v print all lined do not match regexs. this is an important and
useful option.you want to use regular expression, not only to select
information but also to elimilate information. using -v inverts(颠倒,翻转)
the output this way.
-o, --only-matching Show only the part of a matching line that matches PATTERN.
-R, -r, --recursive Read all files under each directory, recursively; this is equivalent to the -d recurse option.
regular expression
匹配文件名的通配符
* 匹配前面的子表达式零次或多次。要匹配 * 字符，请使用 \*。
? 匹配前面的子表达式零次或一次，或指明一个非贪婪限定符。要匹配 ? 字符，请使用 \?。
[abc] 字符集合。匹配所包含的任意一个字符。例如， '[abc]' 可以匹配 "plain" 中的 'a'。
[!abc] 负值字符集合。匹配未包含的任意字符。例如， '[^abc]' 可以匹配 "plain" 中的'p'。
[a-z] 字符范围。匹配指定范围内的任意字符。例如，'[a-z]' 可以匹配 'a' 到 'z' 范围内的任意小写字母字符。
[!a-z] 负值字符范围。匹配任何不在指定范围内的任意字符。例如，'[^a-z]' 可以匹配任何不在 'a' 到 'z' 范围内的任意字符
{flag1,fiag2,flag3....} crate strings flag1,flag2,flag3,etc.for
example,file_{one,two,three} yields the strings
file_one,file_two,file_three.this is a special operator named brace
expansion.that can be used to match filenames but isn't examine directories for existing files to match.instead,it will expand any string.for example,it can be used with echo to yield strings totally unrelated to existing filenames
echo string_{a,b,c} string_a,string_b,string_c
example:
find /home file[a-z1-9]
find /home file[!a-o1-8]
find /home file?
find /home file*
less file{1,2,3}
匹配文件内容的通配符
* 匹配前面的子表达式零次或多次。要匹配 * 字符，请使用 \*。
+ 匹配前面的子表达式一次或多次。要匹配 + 字符，请使用 \+。must have option -E
. 匹配除换行符 \n之外的任何单字符。要匹配 .，请使用 \。
? 匹配前面的子表达式零次或一次，或指明一个非贪婪限定符。要匹配 ? 字符，请使用 \?。must have the option -E. otherwise have no result.
[ 匹配输入字符串的开始位置，除非在方括号表达式中使用，此时它表示不接受该字符集合。要匹配 ^ 字符本身，请使用 \^。
{ 标记限定符表达式的开始。要匹配 {，请使用 \{。
| 指明两项之间的一个选择。要匹配 |，请使用 \|。
\{n,m\} m 和 n 均为非负整数，其中n <= m。最少匹配 n 次且最多匹配 m 次。例如，"o\{1,3\}" 将匹配 "fooooood" 中的前三个 o。'o\{0,1\}' 等价于 'o?'。请注意在逗号和两个数之间不能有空格。
\{n,\} n 是一个非负整数。至少匹配n 次。例如，'o\{2,\}' 不能匹配 "Bob" 中的 'o'，但能匹配 "foooood" 中的所有 o。'o{1,}' 等价于 'o+'。'o{0,}' 则等价于 'o*',enu[0-9][0-9]等价于 enu[0-9]\{2\}.
\{n\} n 是一个非负整数。匹配确定的 n 次。例如，'o\{2\}' 不能匹配 "Bob" 中的 'o'，但是能匹配 "food" 中的两个 o。
+ 匹配前面的子表达式一次或多次。例如，'zo+' 能匹配 "zo" 以及 "zoo"，但不能匹配 "z"。+ 等价于 \{1,\}。
^ 匹配输入字符串的开始位置。
$ 匹配输入字符串的结束位置。
[abc] 字符集合。匹配所包含的任意一个字符。例如， '[abc]' 可以匹配 "plain" 中的 'a'。
[^abc] 负值字符集合。匹配未包含的任意字符。例如， '[^abc]' 可以匹配 "plain" 中的'p'。
[a-z] 字符范围。匹配指定范围内的任意字符。例如，'[a-z]' 可以匹配 'a' 到 'z' 范围内的任意小写字母字符。
[^a-z] 负值字符范围。匹配任何不在指定范围内的任意字符。例如，'[^a-z]' 可以匹配任何不在 'a' 到 'z' 范围内的任意字符
\d 匹配一个数字字符。等价于 [0-9]
\D 匹配一个非数字字符。等价于 [^0-9]。
() 标记一个子表达式的开始和结束位置。
echo string_{a,b,c} string_a,string_b,string_c
for example:ls con*/*/inv*.txt
\<word\> match word. the backslash are required and enable this interpretation of < and >
| alternation(交替,轮流). match either the regex specified before or after the vertical bar. this modifier is an modifier is an "extended" feature and available in grep only when the -E command-line option is used
? match zero or one instance of the precedeing regex. this modifier is an "extended" feature and available in grep only when the -E command-line option is used.
+ match one or more instances of the preceding regex. this modifier is an "extended" feature and available in grep only when the -E command-line option is used
for example
display all line from file1 contain '111'.'1111' or '11111' on a line by itself:
grep '^1\{3,5\}$' file1
display all line from file1 contain "happy", "Happy", "sad", "Sad", "Angry" or "angry":
grep -E '[Hh]appy|[Ss]ad|[Aa]ngry' file1
display all lines from file1 that contain two or more adjacent(邻近的,毗邻的) digits:
grep '[0-9][0-9][0-9]*' file1
display all lines from file1 where the string "linux" appears at the start of the line
grep '^linux' file1
display lines in file1 where the last character is an 'x':
prep 'x$' file1
display the number of empty lines in file1 with nothig between the begin and the end:
grep -c '^$' file1
display all lines from file1 containing only the world "null" by itself
grep '^null$' file1
display all lines from file1 that beginning with any single character other than a digit:
grep '^[^0-9]' file1
display all nonblank lines from file1
grep '.' file1
display all line from file1 with three or more characters on a line(exclude the newline character)
grep '...' file1
display all line from file that contain "file"(because ?(question mark) can match zero more occurrences), file1 or file2:
grep -E 'file[12]?' file1
display all lines from file1 that contain at least a digit
grep -E '[0-9]+' file1
|
